var pet = {
  name: 'andy',
  say: function(say) {
    console.log(say + ' ' +this.name);
  }
};

name = 'global';
// 与上面相同
// global.name = 'global';

var dog = {
  name: 'dog'
};

pet.say.call(); // undefined global
pet.say.call(global,'hello'); // hello global
pet.say.call(dog,'hello');// hello dog
